The so-called tandem type color printer is known as an electrophotographic color printer formed by parallelly arranging photosensitive drums corresponding to yellow, magenta, cyan and black respectively.
The tandem type color printer includes a developing roller opposed to each photosensitive drum. An electrostatic latent image is formed on the surface of the photosensitive drum. When the electrostatic latent image is opposed to the developing roller following rotation of the photosensitive drum, the developing roller feeds a toner to the electrostatic latent image. Thus, a toner image is formed on the surface of the photosensitive drum. A sheet is transported by a belt to be successively opposed to the photosensitive drums respectively. Toner images of the corresponding colors are formed on the photosensitive drums respectively and transferred to the sheet in a superposed manner, to form a color image on the sheet.
A color printer having four photosensitive drums integrally mountable on/detachable from a main body casing is proposed as such a tandem type color printer.
The color printer according to this proposal includes drum subunits retaining the photosensitive drums respectively and a pair of side plates retaining these drum subunits from both sides in an axial direction of the photosensitive drums. Developer cartridges retaining developing rollers are detachably mounted between the side plates correspondingly to the drum subunits respectively. The drum subunits, the developer cartridges and the pair of side plates are detachably mounted on the main body casing as a drum unit.
Both end portions of the drum shafts of the photosensitive drums protrude outward from both side surfaces of the drum subunits. Four axial holes are formed on each side plate at regular intervals along a direction of the arrangement of the photosensitive drums. The end portions of the drum shafts are so inserted into the axial holes as to position the drum shafts (photosensitive drums).
In the image forming apparatus, the formed images are disordered if the surfaces of the photosensitive drums are damaged or foreign matter adheres thereto. If the surface of any photosensitive drum is damaged or foreign matter adheres thereto in assembling or use of the image forming apparatus, therefore, this photosensitive drum must be exchanged.
In the image forming apparatus according to the aforementioned proposal, however, both end portions of the shafts of the photosensitive drums are inserted into the axial holes of the pair of side plates. If it is necessary to exchange one of the photosensitive drums after assembling of the drum unit, therefore, this photosensitive drum cannot be independently removed from the space between the pair of side plates, but the pair of side plates must be detached from all drum subunits to disconnect the drum subunits therefrom. Therefore, it takes time to exchange the photosensitive drum. After the photosensitive drum is exchanged, further, each side plate must be mounted on the four drum subunits, and hence it takes time to reassemble the image forming apparatus.